悬臂式抗滑桩加固黏土边坡地震永久位移算法

为了有效地确定悬臂式抗滑桩加固的黏土边坡地震永久位移,基于极限分析上限定理,针对圆弧滑动式土坡破坏模式,通过对设置抗滑桩条件下土坡进行外力功率和内能耗散率的计算,按严格力学定义推导出坡体在地震作用下的安全系数,进而导出与安全系数相对应的边坡地震屈服加速度计算公式,并结合Newmark滑块位移法对边坡产生的转动加速度进行二次积分,推导出与边坡设计安全系数密切相关的坡体地震永久位移的详细计算公式。以5.12汶川地震卧龙测站东向地震波为例,通过对一算例边坡进行分析,给出了边坡永久位移时程曲线以及不同设计安全系数与永久位移的关系,分析了算法与Ambraseys算法的结果,验证了所提计算方法的有效性,并得到不同设计安全系数时边坡土体黏聚力和内摩擦角对坡体永久位移的影响规律。研究结果表明,坡体永久位移随着设计安全系数的增加逐渐呈指数函数式减小变化,在较低设计安全系数下,坡体永久位移受土体抗剪强度参数影响较为敏感,随着设计安全系数的提高,这种敏感性则逐渐降低。     

地震作用下堆积体边坡的坡面变形与失稳机制

地震作用下堆积体边坡的动力响应特性十分复杂,单一抗震安全系数不足以评价其动力稳定性。通过大型振动台试验,研究了连续多级地震荷载作用下,地震波的类型、卓越频率及峰值加速度对堆积体边坡坡面永久位移的影响,并初步分析其失稳机制。试验结果表明,相同峰值加速度下振动型地震波比冲击型地震波更容易产生坡面永久位移,地震波卓越频率对坡面永久位移也有重要影响;堆积体边坡在峰值加速度apeak=0.2g时开始有大颗粒石砾滚落,对应的坡面永久位移在apeak=0.2g～0.3g之间开始产生并显著增大,另外利用考虑坡面几何形态变化的改进Newmark法对坡顶的永久位移进行了估算。通过坡面永久位移评价堆积体边坡的动力稳定性有一定合理性。     

考虑土体抗拉强度的边坡永久位移极限分析

通过野外观测与室内试验发现,边坡后缘往往存在拉应力区。拉应力区的存在会影响边坡的稳定性,而地震荷载的存在会放大这种影响。分析拉应力区对边坡稳定性的影响,当前主要采用的方式为:对强度准则中抗拉强度进行折减（即张拉截断）。文章通过极限分析上限原理和拟静力法,推导出边坡临界加速度计算方程。以边坡在不同参数组合下的位移系数为基础,输入实测地震波,采用改进的Newmark法对边坡进行位移分析。文章算例的结果表明:拉应力区的存在会大大降低边坡临界加速度,土体在完全张拉截断下的临界加速度对边坡可能会产生超过50%的折减。拉应力区的存在也可以使永久位移达到传统的摩尔库伦理论计算值的2倍之多。文中所有的结果皆以图表形式展示,非常便于理解以及读取数据。      

Seismic reliability analysis of earth slopes under short term stability conditions

Different models were developed for evaluating the probabilistic three-dimensional (3-D) stability analysis of earth slopes and embankments under earthquake loading. The 3-D slope stability model assumed is that of a simple cylindrical failure surface. The probabilistic models evaluate the probability of failure under seismic loading considering the randomness of earthquake occurrence, and earthquake induced acceleration and uncertainties stemming from the discrepancies between laboratory-measured and in-situ values of shear strength parameters. The models also takes into consideration the spatial variabilities and correlations of soil properties. The probabilistic analysis and design approach is capable of obtaining the 2-D and 3-D static and dynamic safety factors, the probability of slope failure, the earthquake induced acceleration coefficient, the yield acceleration coefficient, the earthquake induced displacement, and the probability of allowable displacement exceedance taking into account the local site effect. The approach is applied to a well known landslide case: Congress Street Landslide in Chicago. A sensitivity analysis was conducted on the different parameters involved in the models by applying those models to the Congress Street landslide considering different levels of seismic hazard. Also, a sensitivity analysis was carried out to study the sensitivity of computed results to input parameters of undrained shear strength, and corrective factors. A comparison was made between the different models of failure. The parametric study revealed that the hypocentral distance and earthquake magnitude have major influence on the earthquake induced displacement, probability of failure and dynamic 2-D and 3-D safety factors.     

地震作用下土钉支护边坡震后位移分析

基于土钉弹性支座假设,考虑了地震作用时边坡滑动体实时动态滑移对土钉受力的影响,结合拟静力极限平衡法推导了土钉受力实时动态变化与边坡震后位移计算表达式,提出了一种地震作用下土钉支护边坡震后位移计算的改进方法。结合算例分析表明,考虑与不考虑土钉受力实时动态变化的两种计算方法获得的边坡水平位移时程曲线规律基本一致,皆呈阶跃式增大趋势,但考虑土钉受力实时动态变化的改进计算方法得出的震后位移较不考虑的结果小,两种方法计算结果的差异随着土坡整体稳定性的提高而逐渐减小。结合相关文献中土钉支护边坡振动台试验数据,验证了改进方法的合理性。     

地震作用下预应力锚索边坡的稳定性分析

稳定性分析对边坡工程具有重要的意义。为探究地震对预应力锚固边坡的影响,基于预应力锚索具有安全储备的特点,分析了地震作用下边坡的分阶段模型。在传统Newmark法的基础上,采用拟动力计算,推导了顺层岩质边坡的位移、锚固力和安全系数计算公式。结合工程两个算例,探究了不同锚索模型和地震累积作用下的边坡变形规律。由结果可知,当锚索锚固力取固定值时,边坡计算位移偏大,随时间呈线性增长。当考虑锚索的安全储备时,位移增长速率随时间逐渐减小,最后趋近于定值。不同锚索模型对位移影响较大,锚索储备作用不可忽略。同时地震会对预应力锚固边坡产生永久性影响。当再次发生扰动时,其表现为临界滑动阈值的提升,位移增长率与受震经历的加速度幅值呈反指数变化。以露天矿区边坡为背景,在抗震设防标准下确定最佳支护方案。     

A simplified approach for studying the influence of vertical accelerations on seismic response of slopes

ABSTRACT

A simplified approach is presented for estimating permanent displacements in slopes as a result of both vertical and horizontal seismic accelerations. A study of 52 earthquake records showed that the time difference between maximum horizontal and vertical accelerations varied between 0 and 10.3 s. The approach is illustrated for an earth dam embankment by analysing the effects of five of the above earthquake records. The approach combines a pseudo-static slope stability analysis for estimation of the critical (or yield) horizontal-vertical acceleration combinations, and a Newmark type displacement analysis. Guidelines are presented for conservative choice of soil strength parameters of saturated clays for use in the stability analysis. While permanent displacements of up to 40 cm were predicted without considering the vertical acceleration component, no additional displacement above 3.5 cm resulted when this component was included. The predicted additional displacement was consistently less than 10%, and in 50% of the analyses, vertical acceleration led to smaller predicted displacements. The simple approach may be applied in analysis for any slope using real earthquake records. Using existing, empirical expressions for permanent displacement, based only on horizontal accelerations, the effect of the vertical accelerations may be conservatively estimated by increasing the displacement by 10%.     

SARETL: an expert system for probabilistic displacement-based dynamic 3-D slope stability analysis and remediation of earthquake triggered landslides

 Different models were developed for evaluating the probabilistic three-dimensional (3-D) stability analysis of earth slopes and embankments under earthquake loading using both the safety factor and the displacement criteria of slope failure. In the 3-D analysis, the critical and total slope widths become two new and important parameters. The probabilistic models evaluate the probability of failure under seismic loading and consider the different sources of uncertainties involved in the problem, i.e. uncertainties stemming from the discrepancies between laboratory-measured and in situ values of shear strength parameters, randomness of earthquake occurrence, and earthquake-induced acceleration. The models also take into consideration the spatial variabilities and correlations of soil properties. The developed models are incorporated in a computer program, PTDDSSA (probabilistic three-dimensional dynamic slope stability analysis). These developed analysis/design procedures are incorporated within a code named SARETL (stability analysis and remediation of earthquake-triggered landslides) that was developed in this study for stability analysis and remediation of earthquake-triggered landslides. In addition to the dynamic inertia forces; the developed system takes into consideration the local site effects. The code is capable of: 1. Prediction of permanent deformations that result from landslides under seismic loading using both probabilistic and deterministic approaches. 2. The assessment of landslide hazard that affects major transportation routes in the event of earthquakes, and the preparation of earthquake-induced landslide hazard maps (i.e. maps that show expected displacements and probability of slope/embankments failure) for different earthquakes magnitudes and environmental conditions. 3. Proposing a mitigation strategy against landslides and suggesting guidelines for remedial measures. The developed expert system is applied to a major highway case study. Design maps are developed for the highway under seismic loading. Received: 18 March 1999 · Accepted: 11 October 1999     

基于振动台试验的加速度积分位移方法可靠性研究

土体应变变形是土工测试技术的重要难题之一,加速度积分位移是目前动荷载下原位监测和模型试验中认识土体剪应变响应的一种普遍方法,但缺乏验证与可靠性研究。设计砂质边坡?摇臂?质量块振动台模型试验,实测两地震荷载下多组工况的质量块加速度与位移响应时程,探讨了4种代表性方法求解动态、永久位移的可靠性及偏转影响。结果表明,动态位移求解采用高通滤波是一种可靠途径且受积分方式影响较小,各方法在动态位移工况中积分位移与实测相比,峰值平均误差小于等于25%;双拟法积分位移发生严重偏离,与函数形式和处理过程相关。永久位移求解采用高通滤波导致加速度低频成分缺失而无法得到永久位移;双拟法积分位移与实测相比吻合较好,两地震荷载中误差分别为7%和5%;偏转对动态位移求解可靠性影响较小,但对永久位移影响严重,双拟法呈现发散而失真。试验方法与结论,对认识加速度积分位移求取土体剪应变的可靠性和合理选取数据分析方法具有重要科学价值和指导意义。     

多级支护边坡屈服加速度及因素敏感性分析

基于拟静力法,结合塑性极限分析上限定理和强度折减技术,推导了桩板式挡墙与二级锚杆挡墙支护高边坡地震作用下的水平屈服加速度系数的上限解,分别计算了多级支护结构总高度、边坡平台宽度、土的抗剪强度折减系数、桩板墙桩侧土压力分布经验系数、锚杆挡墙倾角、锚杆轴力及倾角等因素下,多级支护边坡的水平屈服加速度系数的临界极限值。根据正交分析法,给出了地震条件下基覆边坡水平屈服加速度系数影响因素的敏感性顺序。研究表明,多级支挡结构高度和锚杆轴力敏感性较大,而锚杆倾角、桩侧土压力分布经验系数和边坡平台宽度的敏感性较小。锚杆倾角、锚杆挡墙倾角、边坡平台宽度、桩板墙抗力及桩侧土压力分布形式的选择等,对水平屈服加速度系数的影响较小。土的抗剪强度参数中,黏聚力对水平屈服加速度系数的影响较小,而内摩擦角的影响较大。     

三维边坡地震永久位移初探

将著名的Newmark有限滑动位移法拓展到三维空间,提出了三维边坡地震永久位移的分析方法。针对潜在滑体,运用三维极限平衡理论确定屈服加速度,借助数值方法获得平均地震加速度,进而依据Newmark的建议计算永久位移量。实例分析表明,该方法计算结果合理;与三维方法相比,二维分析得到的屈服加速度与平均加速度均偏低,永久位移量偏大;偏差量随着滑体长度的增大逐渐减小     

加筋土挡墙地震稳定性的拟动力分析

为研究不同筋材条件下加筋土挡墙地震稳定性,采用两种简化破裂面形式;由于拟静力法的局限和加筋土挡墙的成层特性,对水平和竖向地震力同时作用下的加筋土挡墙,运用拟动力法和水平条分法推导出其筋材拉力总和与临界破裂角的计算公式。算例分析结果表明,筋材拉力总和随着地震加速系数、回填土重度或者滑动体上部超载的增大而增大;随着土体内摩擦角或者填土黏聚力的增大而减小;当条件相同时,可延展性筋材所承受的筋材拉力总和大于不可延展性筋材所承受的。与拟静力法和规范中的方法比较,基于拟动力法的加筋土挡墙的设计也更加经济。     

Seismic stability analyses for landfill cover systems under different seepage buildup conditions

Drainage of landfill cover systems is often inadequate and buildup of seepage forces can occur over time. However, in most design analyses the seepage buildup is neglected and assumed to have only a minor impact on the seismic performance of landfill cover systems. Actually, simply ignoring the seepage buildup will lead to serious overestimation of the factor of safety. A new two-wedge method was developed to analyze the seismic stability of landfill cover systems under different seepage buildup conditions. The solutions of the factor of safety and the yield acceleration coefficient can be obtained, and the permanent displacement of landfill cover systems can also be calculated using the Newmark method. Based on the developed seismic analysis method, the effects of a parametric variation on the seismic stability and permanent displacement of landfill cover systems are presented.     

加筋土边坡地震稳定性动点安全系数分析方法

对于地震作用下的土工合成材料加筋土边坡,边坡内部结构的动力响应十分复杂,按照已有的安全系数的方法评价比较困难。结合安全储备系数的原理,并考虑到水平方向和竖直方向地震荷载的共同作用,提出求解加筋土边坡地震稳定性的动点安全系数时程分析方法。在理论分析的基础上,分别定义加筋土边坡土体、土工合成材料和筋-土界面的动点安全系数,并建立数值模型。根据所定义的动点安全系数,在计算过程中使用开发的计算工具对动力响应过程中的动力特性数据进行记录、计算和存储,得到加筋土边坡数值模型在地震荷载作用下的动点安全系数。分析结果表明：动点安全系数时程分析方法具有良好的工程适用性;动点安全系数时程分析方法对复杂的加筋土边坡工程进行的地震稳定性分析考虑了加筋土边坡不同结构的综合稳定性,比现有的分析方法更明确地反应出加筋土边坡工程中相对薄弱的结构,对加筋土边坡工程的抗震设计提供一定参考价值;相比水平方向的地震,竖直方向的地震作用对加筋土边坡中筋材和筋-土界面的稳定性影响较大,但对加筋土边坡土体稳定性影响较小。     

锚索框架梁加固平面滑动型边坡地震动力响应

设计并完成了一个缩尺比例为1:20的锚索框架梁加固平面滑动型边坡的振动台试验,通过改变输入地震波类型和峰值,研究了边坡体及支护结构的动力响应特性。试验结果表明：锚固边坡体的整体稳定性较好,地震造成的破坏主要为滑体顶部震碎和无约束坡面岩土体剥蚀、掉块;地震波在经过软弱夹层时存在能量聚集效应,不同地震波下滑体重心处加速度放大系数的差异性随输入地震波峰值的增加而减小;锚索在地震时表现出协同工作的特性,预应力损失最先发生在坡顶,然后向坡体中下部转移;在锚索框架梁的抗震设计时,应考虑边坡体上部的加速度放大效应和锚索预应力损失对边坡整体稳定性的影响。试验结果为合理考虑预应力锚索框架梁的抗震设计提供有益的参考。     

Seismically induced landslide displacements: a predictive model

Newmark's model for predicting earthquake-induced landslide displacements provides a simple way to predict the coseismic displacements affecting a sliding mass subject to earthquake loading. In this model, seismic slope stability is measured in terms of critical acceleration, which depends on the mechanical soil properties, pore-pressure distribution, and slope geometry. The triggering seismic forces are investigated in terms of energy radiation from the source, propagation, and site effects, based on 190 accelerometric recordings from 17 Italian earthquakes with magnitudes between 4.5 and 6.8. The method is based on the calibration of relations having the general form of an attenuation law that relates the energy of the seismic forces to the dynamic shear resistances of the sliding mass to propagate the expected landslide displacements as an inverse function of the distance from the fault rupture; the amount of displacement computed through these relations provides a criterion to predict the occurrence of slope failures. Finally, maps showing, in a deterministic and a probabilistic way, the potential of seismically induced landslide displacements are displayed as a tool to provide seismic landslide scenarios and earthquake-induced landslide hazard maps, respectively.     

地震动作用下均匀土质边坡的临界转角分析

均质土坡变形的整体旋转角度（即转角）与其弧形滑动特征相协调,是比永久位移更为优越的土坡变形与稳定性表征量。地震动瞬态弹性变形应变能相当于土坡系统势能的动态随机性“涨落”,临界点（临界转角）作为系统本身的一个固有特性,不受地震动随机性“涨落”的影响,土坡滑动失稳的临界转角实质上对应着系统势能的突变点。基于均质土坡地震动失稳的特点,结合突变理论,给出了确定失稳临界转角的计算公式,发现其仅与滑带介质本构模型参数 、 和滑弧半径R有关,但在本质上体现了诸因素的影响而具有广泛适用性。     

Performance-based assessment of earthquake-induced catastrophic landslide hazard in liquefiable soils

This paper outlines a methodology for evaluating the likelihood of catastrophic landslide occurrence on gentle slopes in liquefiable soils during earthquake. The approach is based on a modified Newmark sliding block model of assessing the earthquake-induced undrained landslide displacements for conditions of no shear stress reversals on the sliding surface. By employing the shear resistance-displacement relationship from undrained monotonic ring shear tests, the simulation model incorporates the sensitivity of computed displacements to variations in yield acceleration. The proposed approach involves an examination of undrained seismic slope performance under various horizontal seismic waveforms scaled to different specific values of the peak earthquake acceleration. An example problem illustrates how the proposed methodology may be used to demarcate, based on the magnitude of permanent seismic displacement, the levels of low, moderate and high risk of catastrophic landslide on a gentle slope in a saturated cohesionless soil susceptible to liquefaction during earthquake.     

卫生填埋场复合边坡地震稳定性和永久变形分析

采用非连续变形分析方法,对卫生填埋场复合型边坡的地震稳定性和永久变形进行了详细地计算分析,探讨了边坡倾角、土与土工膜之间的摩擦系数、边坡的长度、覆盖土层的厚度以及地震加速度对边坡的稳定性和永久变形的影响。由边坡的破坏形式,讨论了复合型边坡的破坏机理,指出了文献[1]给出的计算公式的适用条件以及局限性,为卫生填埋场复合型衬垫层的稳定设计提供参考。     

Seismic stability analysis of piled embankments: A multiphase approach

The seismic stability analysis of an embankment lying over a soft foundation soil reinforced by a group of vertical piles is performed within the framework of the upper bound kinematic approach of yield design. The analysis is based on a previously developed ‘multiphase’ model of the reinforced ground, which explicitly accounts for the shear and bending resistances of the piles. Making use of appropriate failure mechanisms involving shear zones across which the reinforcements are continuously deforming, along with ‘plastic hinge’ surfaces, upper bound estimates to the critical seismic coefficient of the structure are derived. The results, which are confirmed by the simulations obtained from a finite element elastoplastic code, give clear evidence of the key role played by the bending strength capacities of the piles in ensuring the stability of the pile reinforced embankment. Copyright © 2009 John Wiley & Sons, Ltd.